1. Field of the Invention
The present invention relates generally to methods and compositions for systemic administration of parathyroid hormone to mammalian hosts. More particularly, the present invention relates to pulmonary administration of active parathyroid hormone fragments to provide pulsatile serum concentration profiles.
Human parathyroid hormone (PTH) is an 84 amino acid protein that is involved in calcium and phosphorus homeostasis and control of bone growth and density. N-terminal fragments of PTH, particularly those consisting of amino acids 1-34 and 1-38, retain the full biological activity of the intact protein. Recently, the use of PTH and PTH fragments in combination with vitamin D or dietary calcium was found to be effective in the treatment of osteoporosis when administered to a host on a periodic, preferably daily, basis.
Heretofore, the administration of PTH and PTH fragments has generally been accomplished subcutaneously, i.e., through injection. The need to inject PTH (or any other drug) on a daily basis, however, is undesirable. Most patients have an aversion to self-injection of drugs, and the need to visit a clinic or doctor's office for administration is inconvenient and burdensome. While other forms of administration have been suggested, such as oral delivery to the stomach, transdermal delivery, and nasopharyngeal absorption, none of these delivery routes has been proven to be effective and each suffers from certain drawbacks. Oral delivery results in very low bioavailability of polypeptide drugs, usually below 1%, due to degradation in the gastrointestinal tract. Moreover, the epithelial lining of the gastrointestinal tract is impermeable to most polypeptides. Nasopharyngeal and transdermal delivery avoid the problems of enzyme degradation, but usually require penetration enhancers in order to effect systemic absorption. Even with such penetration enhancers, bioavailability will usually be very low, and the penetration enhancers can often cause undesirable irritation. In the case of nasopharyngeal administration, penetration enhancers can often damage the nasal epithelium and chronic use has been associated with hyperplasia of the nasal lining.
Pulmonary or respiratory delivery of polypeptide drugs has also been suggested. Relatively large proteins, such as growth factors and cytokines which are typically larger than 150 amino acids, are often readily absorbed through the cellular lining of the alveolar region of the mammalian lung. Advantageously, such absorption can be achieved without the use of penetration enhancers. The pulmonary absorption of smaller proteins, usually below 100 amino acids in length, is much less predictable. Many smaller native polypeptides are not absorbed by the mammalian lung, but certain examples such as insulin (51 amino acids) and calcitonin (32 amino acids) have been found to be systemically absorbed when delivered to the lung. Even when a protein drug is systemically absorbed by a host through the lung, the pharmacological kinetics of the drug are unpredictable. Thus, both the amount and timing of drug bioavailability are unpredictable.
It is presently believed that PTH is most effectively delivered to a patient in a pulsatile fashion. That is, serum concentrations of PTH should rise rapidly after administration and fall rapidly after a peak has been reached, generally resulting in a spike in the serum concentration profile. Thus, it is advantageous for any route of PTH delivery to provide such a serum concentration profile.
For these reasons, it would be desirable to provide alternative delivery methods for parathyroid hormone which are patient acceptable. Such methods should avoid subcutaneous injection, limit irritation to the skin and body mucosa, and provide a desired pulsatile delivery profile discussed above. Such methods should further provide for high levels of PTH bioavailability, be amenable to self-administration by the patient, and be economic.
2. Description of the Background Art
U.S. Pat. Nos. 4,833,125 and 4,698,328, describe the administration of active parathyroid hormone fragments in combination with vitamin D or a dietary calcium supplement. Suggested administration routes include parenteral by injection, rapid infusion, nasopharyngeal absorption, dermal absorption, or oral. See also, Neer et al. (1987) Osteoporosis 53:829-835. U.S. Pat. No. 5,011,678, describes the use of amphophilic steroids as a penetration enhancer for nasal or bronchopulmonary delivery of proteins and polypeptides, listing parathyroid hormone as one of a "veritable host" of proteins which could be delivered with the enhancer. Parathyroid hormone (full length) is secreted naturally from the parathyroid gland as a series of spikes in a pulsatile fashion which is analogous to pituitary hormones (Harms et al. (1987) Int. Symp. on Osteoporosis, Aalborg, Abstract 232). The full length hormone is rapidly broken down in the circulation to several fragments which are the dominant serum forms. It is hypothesized that an intermittent or pulsatile secretion pattern for parathyroid hormone is necessary to maintain its bone restoring properties (Hesch et al. (1988) Calcif. Tissue Int. 42:341-344 and Habener et al. (1971) Proc. Natl. Acad. Sci. USA 68:2986-2991). Patton and Platz (1992) Adv. Drug Deliver. Rev. 8:179-196. describe methods for delivering proteins and polypeptides by inhalation through the deep lung.